Mixing heads are known, for example, from U.S. Pat. Nos. 3,975,128 and 4,175,874, in which the flow of mixture issuing from a mixing chamber is deflected at a right angle into a relatively short stabilizing channel and then into a molding cavity or the like. An ejection piston is associated with the stabilizing channel, the head and shaft of this piston consisting of a single, equally strong piece which corresponds in diameter to that of the stabilizing channel. The hydraulic piston which is positioned on the rear end of this piston and is bilaterally chargeable is larger in diameter than the piston itself. In this apparatus, the stabilizing channel is located in a tubular housing and serves only to stabilize the reaction mixture issuing turbulently out of the mixing chamber, so that the mixture may enter into the molding cavity in a laminar flow from the stabilizing channel.
For different applications, it is sensible to provide a comparatively long connection piece between the mixing head and the molding cavity, in order to allow the apparatus to be attached more easily to the respective inlet opening of the particular molding cavity, for example, in the case of multi-layer presses. A connection piece of this type is approximately from 0.2 to 2 m long and, preferably, from 0.5 to 1 m long. Hitherto, the operation has been managed by using filling tubes of a corresponding length which then had to be freed from the remnants of the mixture by mechanical means or by using a rinsing agent. Inexpensive tubes have been also used for such purposes and after limited use have been thrown away.
These known apparatuses have the disadvantages of being relatively expensive and require a rinsing agent or expendable tubes. They also cause a considerable amount of reaction mixture to be lost.
Use of the apparatuses with the stabilizing channels from U.S. Pat. Nos. 3,975,128 and 4,175,874 is ruled out when a long connection piece is necessary because the previously known type of ejection piston can only be of a short length. Ejection pistons of longer length become blocked by the film which forms with time on the inside wall of the stabilizing channel. In spite of a good cleaning effect by the ejection piston, this film cannot be completely avoided.
The object of this invention is to provide an apparatus with which mold cavities may be filled without loss of reaction mixture and without involving a substantial working expense or the use of rinsing agents via a relatively long connection piece.